[R-390] Re: Spurious Resonances

[Bob Camp]

Hi

What are you picking off the output with?

Picking off at the plate would be a *much* better idea if you are  
trying to measure the input circuit. You will have far less impact  
from the probe that way. If you want to suppress the effect of the  
output tank, swamp it with a low probe impedance.

Bob


On Oct 27, 2007, at 10:35 AM, Tony Casorso wrote:

> How lucky can I get? I posted a set of images this morning that had  
> a "spurious response" in it. It turns out it was cause by the  
> settings on my sweeper (DC Offset was cranked over to one side for  
> some reason). The mailer wus unable to post it for some reason so I  
> get to try again with good pictures.
>
> Here are links to couple of pictures. I am sweeping the preselector  
> in my R-390a. The left edge of the sweep is 1.5MHz. The right edge  
> is 4.5MHz. The center is approximately 3MHz. The receiver is tuned  
> to 3.00MHz and the power is off. I am measuring the response at the  
> grid of the RF stage.
>
> The broader response picture is with the 25 Ohm (gen with 50 Ohm  
> rterminator) sweep gen directly connected to the balanced input. The  
> sharper response is with a 2.2K resistor in series with one side of  
> the balanced input.
>
> It looks like I was right that low source impedance broadens the  
> frontend response.
>
> http://i25.photobucket.com/albums/c90/tonysradios/IMG_0825.jpg
>
> http://i25.photobucket.com/albums/c90/tonysradios/IMG_0826.jpg
>
> Tony
>
> ----- Original Message ----- From: "Tony Casorso" <canthony15 at msn.com>
> To: <r-390 at mailman.qth.net>
> Sent: Saturday, October 27, 2007 8:09 AM
> Subject: [R-390] Re: Spurious Resonances
>
>
> I should havethought about it for a few more minutes.
>
> Maybe the sweeper has a strong second harmonic that is visible near  
> 1.5.
>
> Tony
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